Is the time the same?
If I have Ra-226 source with constant Rn-222 emendation rate, this source placed in closed chamber (50 L) the activity of air Bq/m3 reach to saturation equilibrium after 600 h.
If we placed this source in small chamber (0.5L) is the saturation time the same? Or will activity take a small time to reach saturation?
LRge chambers mimic the actual situation better. Small chambers have problems in the equilibrium state between radon and progeny. It is very important that th
that the chamber is from steinless steel to avoid plate out effects.
Sure I understand u large chamber from steinless steel but small from aluminum I got saturation in large after 500 h as u see in graph I want to know if I can use this time as saturation time for small box or as I think may be it take small time in small chamber?
I see from your diagram a saturation in about 600 h=25 days. Normally you need 28 days to get equilibrium with Ra226 that produces radon (assuming that you have a Ra-226 source and not a radon calibrated glass source). All these pre-assume that (1) there is no plate-out on surfaces (OK with aluminium); (2) there is leakage (rational); (3) you monitor the concentration with a detector in-situ (naJ, AlphaGuard-equivalent); (4) you monitor progeny deposition on paper filters with PIPS detectors, SSNTds etc.
AlphaGuard inside chamber with Ra 226 point standard source with good emanation rate
I wonder in our investigations, we assumed that Radon and its progeny reach equilibrium in 4 hours. Then Why this 600 hours?
It is not necessary that it must be attain in 28 days, sometimes the state can be attain within few hours so the concept of 28 days is just an assumption.
Thanks GARBA. We never measured it but our Mentors in radon studies in India(Ghosh and Bhalla) measured it. I think 28 days is too long?
If the source is Ra it needs time to attain full equibrium with radon and progeny.
If it i radon calubrated vial it needs 4 hours.
4 h for Radon progeny in lief measurement its ok but in source of Ra as our case it need long time to equilibrium in closed chamber
This is called secular equilibrium or for Rn-222: Rn=k*[1-exp(-t*ln2/half-life(Rn))], where Rn is radon activity, k is proportional to the radium-226 activity, and t is time, and the half-life(Rn) (of radon) is 3.82 days, or more simply, Rn=k*[1-1/2**(t/3.82 days)]. In other words, independent of the chamber size, in 3.82 days Rn activity is at 1/2 of its terminal value, at twice the time; 7.64 days, Rn activity is at 3/4 of its terminal activity, at 3*3.82 days or 11.46 days, Rn is at 1-1/2**3=1-1/8=7/8ths of its terminal activity and so forth. In other words, Rn activity is at 99% of its terminal activity in 609 hours (=3.82*24*ln100/ln2 hrs).
we use alphaguard in diffusion mode so its clearly by radon alpha not progeny
AlphaGUARD P30 saturates at 30 kBq/m^3, so, from your figure you are using an AlphaGUARD 2000 series. The most you can decrease the volume is to 2 liter without also decreasing the amount of radium used as the detector will saturate at 2000 kBq/m^3. If you wish to use 0.5 liters, decrease the amount of radium by at least 4 times (8 times less would be better).
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